Sports Watches – Lactate Threshold

Ever heard a fellow runner or athlete (which ever sport you choose) say that they couldn’t finish the race because they “hit a wall”? Or their bodies just couldn’t keep going? Or that they are doing a lengthy cool-down (longer than 10 mins) because they need to get rid of the lactate? Or maybe your coach has mentioned one or two of these? Well this last post of the Sports Watches Series (for the moment) will hopefully clarify a few things.

wall-sm
Hitting the wall

Lactate threshold is one of the measurements that your watch will bring up, especially after a longer run (generally < 60 min) and when you’ve really pushed yourself (into the anaerobic HR Zone; > 80% HRmax); and it is represented as a HR (bt.min-1).

So what is this lactate threshold that not just appears on your watch, but invariably something you’ve heard in passing?

To understand the concept of a lactate threshold, I am going to have to give you a “short” explanation of how the human body works, specifically looking at the muscle physiology – what happens inside the muscle when you start exercising…

 

I’m sure we have all heard someone saying that they had to stop exercising because of a build-up of lactic acid, or someone did a lengthy post-race run/cycle, to “get rid of the lactic acid”. But what is lactic acid?

Lactic acid is made up of lactate (La-) and hydrogen ions (H+), and this is a by-product of pyruvate. Pyruvate itself is a product of the breakdown of either glycogen or glucose (see Figure 1).

breakdown-of-glucose-and-glycogen
Figure 1: Breakdown of Glucose and Glycogen

But, let’s go back a few steps to understand the above process:

When we start exercising, our body breaks down glycogen and glucose (carbs) into pyruvate. Pyruvate can either enter the mitochondria* for oxidation (aerobic metabolism requiring oxygen) for more adenosine triphosphate (ATP) (Energy) or can be reduced into lactic acid (anaerobic metabolism).

*Mitochondria = your body’s cells power plants – they produce energy in the form of ATP (adenosine triphosphate)

The lactic acid that we try and “remove” after an event or training, is a weak acid and is very quickly broken down into its two components, namely Lactate and H+ ions, and as a result, there is never much lactic acid in the muscle and even less in the blood. Especially following heavy exercise sessions, the lactic acid levels return back to normal within 1 hr post-exercise, and this time frame is even further reduced following a lower intensity exercise such as jogging or walking or doing absolutely nothing.

Originally, it was thought that as the exercise intensity increased greater than the rate of VO2max, then oxygen-debt (O2-debt) occurs and the metabolism switches from being aerobic (requiring oxygen) to anaerobic (without oxygen). The thought process following this switch was that it resulted in an abrupt increase in blood lactate levels, resulting in what is called metabolic acidosis. All of this lead to people believing that lactic acid was a metabolic waste product that resulted from us pushing our bodies beyond its capacity to deliver adequate O2 to the working muscles.

If you keep the above figure in mind, as the intensity of an exercise session/bout increases, the mitochondria (remember that this is your cells’ power plant) are unable to oxidize (break down/remove hydrogen ions) all of the pyruvate. As a result we have this increased concentration of pyruvate, which in turn triggers the conversion of pyruvate into lactate through an enzyme. The lactate is then broken down further into the H+ ions and lactic acid (La-). It is the increased amount of H+ ions that could depress muscle function, rather than the La-.

Blood lactate can be taken up and utilized as a fuel source for skeletal muscle, as well as the heart, brain, liver and kidneys. It has been shown that 75% of lactate is removed during exercise, with the remaining 25% being converted to ATP through gluconeogenesis (generation of glucose from non-carbohydrate carbon substrates) in the liver and kidneys. In some instances, lactate can be a more preferred fuel source compared to glucose. Interestingly, lactate uptake, although dependent on concentration gradients, is not limited in transport, such as with insulin-dependent glucose; lactate can offer a fast and efficient fuel source. Lactate, therefore, is not a not a waste product, but rather an important source of energy and potentially a signalling molecule that is continuously formed and utilized, even under fully aerobic conditions.

 

blood-lactate-and-vo2
Figure 2: Lactate Threshold – relationship between VO2max, blood lactate and workload.

If we look at the above image, you can see how VO2max increases over time/ with an increase in workload, while lactate remains steady, and then tends to increase exponentially. The turning point is where the lactate threshold is recorded. This is the point at which you almost feel like your body just can’t continue, and it’s completely and utterly trainable.

So why have it measured, and how is it measured?

The best way to measure lactate threshold is while you’re having a VO2max test done, and this is in two ways: 1. By finger-prick/earlobe-prick; or 2. Inferred from the VO2max data analysing the O2 uptake and CO2 expired.  Although your VO2max is limited with train-ability, Lactate Threshold (LT) is something that one can train, and try get it to occur later on in the test. VO2max in this regard is the maximal potential of an athlete, while the LT or pace/power at LT is the athletes current ability. The way one trains the LT to be able to sustain higher workloads for longer before lactate accumulation occurs, can be done by training in high-intensity HR zones or by pace/power which equates to a high-intensity. So in essence, one measures the LT in order to identify two things:

  1. How well-trained you currently are.
  2. How to adapt your training to enable you to sustain high-intensity exercise for longer periods of time.

So if you need to have a VO2max test to help determine this, what does that mean for the LT that my watch gives me? Well, just like how your watch uses an algorithm to determine your VO2max, it uses a similar concept for the LT, by looking at your HR – again, this is just an estimation, and a full test should be done to get accurate measures and training recommendations.

 

Just to wrap up:

  • Lactate is not the cause of fatigue
  • Muscle pain experienced after exercise of high-intensity is caused by ultra-structural damage, inflammation and sensitized nocireceptors – NOT lactate
  • Lactate is a quick, efficient source of energy for skeletal muscle, the heart, liver and kidneys
  • Fatigue is multi-faceted and cannot be narrowed down to just one cause

 

If you would like to book or inquire regarding the VO2max and lactate testing please feel free to contact me:

 

References:

 

Hall, M.M., Rajasekaran, S., Thomsen, T.W., and Peterson, A.R. (2016). Lactate: Friend or Foe. PMR Journal, 8: S8 – S15.

Gladden, L.B. (2004). Lactate metabolism: A new paradigm for the third millennium. Journal of Physiology, 558 (1): 5 – 30.

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